There are serious applications for this. Namely, being able to orient yourself in space without using propellant is a very valuable ability.

The real surprise is that this is nothing radical; I really don't get why it deserves a press release. Probes have been using momentum wheels, for example, to do the same thing for decades. What is the big advantage of this over, say, a small set of momentum wheels? All I can really say about it is that it's more complex, and seems more likely to wear and have part failures.

I see no completed robot, no performance data or even a simulation of how it will perform in the real world. Just a REAAALLY bad web site (No page navigation? Come on!) and some digital photos of these kids and their drawings. The dates in the pages and some photos are from fall of 2003. If these were college seniors (as it says in the "meet the team" section) at the time they have already graduated by now, and abandoned these pages.

That's not too impressive. They're not even close to active stabilization. All they're doing is rotating a weight that also moves in and out from the axis of rotation to change the moment of inertia. This gets them a little net angular motion. Big deal. I've seen wind-up toys do that.

Since it's a one-axis device, there's no need to test it in a zero-G environment. Hanging it from a string would work equally well.

There's useful work to be done on three-axis stablization algorithms, but this isn't i

Because cats always land on their feet and toast always lands buttered side down, you can construct a perpetual motion machine by simply strapping a slice of buttered toast to a cat's back. When the cat is dropped it will remain suspended and revolve indefinitely due to the opposing forces.

Can we apply some kind of techno-butter to one side to see if the robot can stay in a constant state of airborne suspension?

Bah, can't we put this to rest?

The cat/buttered bread assembly is a hoax. What would and does happen is that the mass of the cat and the ability to land on it's feet far outweigh the attractive forces of the tiny amount of butter to the floor. If you increased the mass of butter to counter the mass of the cat, you would not have a hovering cat/butter object, but something that sl

What would and does happen is that the mass of the cat and the ability to land on it's feet far outweigh the attractive forces of the tiny amount of butter to the floor. If you increased the mass of butter to counter the mass of the cat...

YEA! You do have a sense of humor after all! ^_^

I'm not scientist, but do know that cat's backs do not repulse the floor; if you hang a cat upside down 3" above the floor and drop i

Cats reposition themselves to land on their feet because they can sense the change in velocity (dv/dt = acceleration). My professor stated this only works for small height values (less than 20 ft), otherwise, the acceleration due to gravity might result in an unpleasant aftermath.

I recall reading a bit about how after the 10th floor, cats cat spread thir legs and "glide" to slow down enough to survive. Statistics show that there are more feline fatalities between floors 3-10 then there are after 10.

Speaking of morbidly funny image. That made me remember a little comic strip [ragna-fan.net] I've seen. It is relatively harmless. Has something to do with a cat falling. The landing on the feet part is unconfirmed.

Cats reposition themselves to land on their feet because they can sense the change in velocity (dv/dt = acceleration). My professor stated this only works for small height values (less than 20 ft), otherwise, the acceleration due to gravity might result in an unpleasant aftermath.

Actually, it's the short falls [uaf.edu] that tend to kill cats. Cats (like skydivers) can assume a position that reduces the terminal velocity and presents the greatest surface area for impact, reducing the force per unit of surface area. It takes a while to rotate and get into the position, so if the fall is too short, the cat will land in an awkward position and is far more likely to die.

This is not to say that the cats that fell from a great height were uninjured - just that they were more likely to have non-fatal injuries.

I call bullshit. This study has one HUGE flaw in it. I remember in college when this study was brought up in a statistics class. The flaw can be summed up in one clear thought.

"No one brings a clearly dead cat to the vet."

If the fall is high enough, the odds of living decrease and therefore no cats are brought to the vet unless they miraculously survived. The study self-selects for those cases. Ergo...bad stats. Grrr...the bane of my social sci existence.

That study does have that huge flaw, but I wonder what the terminal velocity of a cat is? If it is low enough then it could survive from any 'reasonable' height (where reasonable means we do not need heat shields for reentry).

I doubt we could convince the ASPCA to give us unadopted cats for the required experiments.

To start with, a study of 115 cats is far from quality data. But given the data, let's take a look a little closer.

First, there is no bell curve in this study. They reported "Three of the cats were dead upon arrival and 8 more died in the next twenty-four hours, leaving 104 living cats or about 90%". All we know is that 104 of the 115 cats survived. There is no data as to the amount of trauma they incurred, so dividing them into 6 groups is pointless.

Ok, so lets conduct an experiment: throw 500 cats from an airplane, say 3,000 ft. above ground level. This way we are certain terminal velocity is attained. Record the bell-curve survival rate. Those on the ground doing the counting, wear a helmet.

I wonder if, given an inverted starting attitude, there is a certain height at which the fall would be less dangerious if it were either higher or lower.

Above this height the cat would have had time to attain a fully non-inverted attitude and so would better cope with higher impact forces. Below this height and although the cat would still be in a bad attitude, the velocity attained would be sufficently small that injury would be less likely.

This experiment would require a standard cat, as I would expect that small, fluffy, long-haired cats with tails would have a lower terminal velocity than enormously fat, bald, tailless cats. Likewise, previously fat cats who had lost substantial amounts of weight would have enough loose, baggy skin might have an advantage above certain velocities, where their excess skin would flap about in the wind, helping keep the velocity down. By stretching out their little arms and legs they might even be able to form little parachutes or planes, with which they could glide safely to the ground, much like a flying squirrel. But bigger. And uglyier.

I've dissected a cat. It was pretty much a standard short haired cat. I think it must have been a stray alley cat, but not one of the bright ones that was smart enough to run like hell when the cat-snatchers came.

Anyway, Once you see a cat without it's skin, the reason that cats can take falls becomes apparent. the only really massive structure in a cat is the legs/shoulderblade/pectorals structure. The shoulder blades on our cat were huge and had an endless number of muscle attachments. The shoulder blad

I remember experimenting with my cat growing up to see how short a height it could recover in over a sofa cushion.

I remember being pretty amazed at how short a distance it could twist around in. I think it was definitely under a foot in height that it could land on its feet in. Anything less it could still manage to land on its side ad least.

I don't think that a fall of about 8 inches could be considered life threating for a cat.

But their project is about " a robot that uses motions and contortions of its body to orient itself in zero gravity" but they describe it using a situation caused by gravity "If you've ever seen a cat land on its feet after falling while upside down then you've seen the idea behind our project."

When a cat is falling ( or while anything is falling for that matter ) it is in free fall until there is significant drag from its motion through the air. Free fall is effectively a zero gravity state.

NASA used planes in a dive to simulate zero gravity for astronaught training.

So that either means the analogy is false, or their robot will use motions and contortions to orient itself, and then commence spinning and wriggling out of control, since there is no "down" in space.

The motions used by a cat to orient itself to land on its feet are completely general and do not depend on the presence of gravity. So the falling cat could orient itself any way it wanted--it just happens to prefer to land on its feet.

But it's generally defined on earth (which is used in the analogy) that gravity will pull the cat towards the earth, either landing on the earth or a structure that is resting on the surface of the earth.

In orbit, of course, the same is true, except that the trajectory is such that the object keeps overshooting the earth.

In fact, that would be interesting to see - if you take a cat up in space, and toss it towards a wall. Mind you, not with force to hurt it. Anyways, would it know at that point to move

The article describes how the cat manages to turn by rotating parts of its body without actually pushing against anything, or breaking any laws of physics. I think NASA would be very interested in this because it would mean a robot in a 0-g environment could alter its rotation without having to resort to firing chemical or compressed gas engines. Which is pretty cool. Has anything else like this been attempted?

I'll admit, though, that my initial thought was that the robot being in a situation where there i

Cool site. I've put this to the test - I hold my cat on her back maybe two feet over my bed, then quickly pull my hands out from under her. It's pretty cool how fast she gets herself righted, but it does seem to disorient her a little, like when I get her to spin around chasing the end of a piece of string.

Cats are ordinarily so graceful that it's hard not to laugh when they do something clumsy.

Just attach a printed list of all the Internet Explorer security holes in the past few months to any existing robot's feet, and the resulting weight should be enough to reproduce this cat-like ability.

That sounds like a fun project to work on. I can think of all sorts of uses for something like this. We can ensure that all olympic divers enter the water perfectly perpendicular to the surface. likewise gymnasts doing the vault will always land on their feet. Throwing spirals with a football could be automagic. Ok...nothing lifechanging there...but I'm sure someone will think of something.

...if the robot can survive terminal velocity falls [uaf.edu] like cats. Cats falling from very high heights (i.e. skyscrapers) tend to survive the fall better than those falling from lower elevations.

I'm no scientist, all I know is that my cat fell from my apartment on the 17th floor and was really fucking dead after that. Where she landed there was no big mess, no blood coming out of her mouth, really pretty clean so I guess her landing was perfect. But at that height it didn't matter.

Obviously my one cat "study" isn't the scientific method, but if your average living mammal falls from 17 floors up, they will mostly fucking die and skys

Yeah, a seventeen floor drop will probably kill a cat. However, skyscraper vs high rise doesn't really matter, as the cat is already at terminal velocity. The observation that dead cats don't get taken to the vet to be counted obviously holds true. Nevertheless, a lot of cats -do- survive such falls, which is still remarkable.

Cats falling from very high heights (i.e. skyscrapers) tend to survive the fall better than those falling from lower elevations.

Um- no. Every bone in their body breaks and their internal organs are crushed, just like a human. The "paper" you cite is an absolute crock of shit- they have TWO datapoints, and among other things, the data-fit is so poor it implies 100% survival rates above 8 stories for cats! BullSHIT! Nevermind that they consider "skyscraper" to be "under 7 stories", when most people cons

No actually, the paper he cited is not the only research that has been done on this - I distincly remember reading an article about this 3 or 4 years ago, and a radio program mentioning it a while back too. I didn't read the paper he pointed to, but the reason it works is because not only do the cats orient themselves properly, they also splay out their legs and stretch the skin out, creating a parachute-like effect which drastically reduces their terminal velocity. Cats falling from 5 stories have plenty o

Like the "Quaddies" in Vorkosigan books Lois McMaster Bujold. Genetically engineered humans with a second set of arms where their legs should be, specially adapted to life in space. Good stories by the way, if you're looking for reading material...

DPA: As professor Fallsonhisface of the chair for human mechanics anounced today, he delivered another breakthrough in robotics. By using a new technology dubbed "artifical clumsiness" he created a robot that appears more humanlike than every other machine today. He stated that "... Most people are scared to death by machines acting perfectly. They will only accept a robot in their daily life if those manage to make mistakes. People want to feel supperior."

He was confident that the first prototype would convince the public once it has been reassembled again.

We tend to see a fair number of these postings coming through here. What I'm trying to get my head around is how all of these fit together.

It would appear that this posting fits in with a robot's ability to manage its own body. I guess other components are intelligence, being able to sense the environment, being self-sufficient, and so forth.

Does anybody have any good thoughts on how everything is fitting together, and how far we are, in total, from a robot that can be truly useful, say, as a human companion, or for other purposes?

In grad school one of my physics professors wrote a paper on orienting onself in zero g with no net angular momentum. One student was just convinced it was impossible.
Soon thereafter we were visted by Story Musgrave (one of astronauts who fixed Hubble) and the professor told him of the paper. Story immediately sat down on a swivel chair and demonstrated the motion necessary to turn in zero g without grabbing on to anything.
It's interesting how a concept that caused some interesting debates among the students suddenly became obvious when it was directly demonstrated.

Sit calmly in a swivel chair, slowly extend your legs, then extend your arms to one side, say to the left, move your arms from that position to the other side of your legs at the same time pull your arms close to your body, at the same time push your pelvis in opposite direction to your arms.There you have it, net angular momentum is 0 but you are still rotating.

No no no. With the swivel chair, you're using an external force - the friction of the chair. You're able (whether you realise it or not) to push against the chair, using the fact that the bearings aren't completely frictionless. (IIRC, the friction is relatively greater for slow rotation.) That's where you can pick up some angular momentum.

If the chair rotated completely frictionlessly, then you wouldn't be able to orient yourself; every time you twisted to put one part of your body one way, the rest

Just curious... how does something "fall" in zero g? Doesn't falling imply gravity?

It also implies zero G. Gravity is present everywhere in the universe, so there is no such thing as the absence of gravity. What "zero G" actually means is "moving freely under the influence of gravity."

Back to the early experiments for a moment of humor. You may have seen a
picture from the late 50's, early 60's of a zero G experiment involving a
cat floating in air in the cockpit of a fighter aircraft, with the oxygen
masked pilot looking on. The one in my science book as a kid showed the
cat twisting in mid air, front paws and rear heading in different
directions as it tried to cope with simulated Zero G. Looks pretty cool,
and I'm sure it made it into more than one textbook deal

It would probably become very confused, but I don't think it would constantly spasm in attempts to right itself like you seem to suggest. A cat's reflex is based on acceleration, which would not be happening. It might assume the "skydiver" position that it would at terminal velocity in a normal fall, as other posts have mentioned.

Now they will finally be ble to create a perpetual motion machine, which not only works, but is environmentally and feline friendly as well.

PETA had this to say:

the desperately needed, perpetual motion machine can now be achieved, that does not conflict with our interests, The long controversial Buttered Cat array [flippyscatpage.com] is now available without the cats, it is indeed a great day for humanity

As an individual who has participated in the RGSFOP program, I have seen a number of novel experiments, but this particular experiment is a retread that has been done many, many times. Last March, for example, Washington-St. Louis did a very interesting experiment involving zero-gravity orientation of a space vehicle. The typical RGSFOP experiment fails, however, although my University did experience a success this year.

As far as I can tell, this is basically an overly complex version of a momentum wheel...basically, a massive, low-speed flywheel. Spin it one way, the surrounding structure spins the opposite direction...stop the momentum wheel, and the entire structure stops spinning. That is, angular momentum for the entire structure is conserved.

The Hubble telescope uses momentum wheels for very precise aiming without requiring propellant and complex, failure-prone, and mirror-dirtying thrusters. These people are trying